Effects of centrally and systemically administered L-tyrosine and L-leucine on ovarian function in the old rat

The effects of centrally and systemically administered L-leucine and L-tyrosine on ovarian function were studied in the old female rat. Systemically administered L-tyrosine reinstated regular vaginal cycling and ovulation, whereas systemically administered L-leucine did not. When administered centrally, through an indwelling cannula in the medial preoptic area, neither L-tyrosine nor L-leucine altered the ovarian or vaginal condition of the old female. When these females were subsequently treated with L-dopa, both systemic and central application were found to reinstate ovarian cycles. Potential mechanisms of action at the level of CNS monoaminergic neurotransmission are discussed.